In a typical computer network there are a number of client computers that are coupled via communication links to several network server resources. These resources include, for example, file servers, print servers, modem servers, and CD ROM servers. Each server is usually a stand-alone computer with its own keyboard, video, and mouse monitor (KVM). Each client computer utilizes the functions provided by the server computers through respective communication links.
In some computer applications, it is desirable to connect one or more users to one or more computers. It is also desirable at times to do so when users and computers are at different locations. For example, users increasingly desire to access information from several computers located at remote locations via a peripheral switch, such as a KVM switch. In such cases, a user could remain at one location and cause the peripheral switch to selectively attach to one of several computers. It is also possible to use peripheral switches to selectively connect several users to a plurality of remote computers.
Video signals produced by a remote computer are routinely transmitted through a KVM (keyboard, mouse, video) extender to a remote user. In one approach, in order to minimize the number of wires extending between a remote computer/server and the remote user location, horizontal and vertical sync signals as well as mode signals are encoded with the analog video signal.
In another approach, a dedicated communication channel is provided from a remote site to serve as a means for coupling to the peripheral switch. The dedicated communication channel could use the same propriety protocol language as the local peripherals for control and status functions. Security features may also be controlled from the remote site. In yet another approach, the method of providing a remote peripheral connection uses a local area network (LAN).
The KVM switches and extenders are known devices and are commercially available. Examples of these KVM switches are commercially marketed by Avocent Corporation of Huntsville, Ala. as the Autoview family of products and the XP family of products. Avocent Corporation also markets KVM switches under the names Outlook and ViewPoint. The KVM switch 12 provides a number of functions in the embodiment of FIG. 1. First, when servers 13 boot up, the KVM switch 12 emulates keyboard, video and mouse initiation commands such that each of the servers 13 believes that it is actually connected to a single keyboard, video and mouse workstation. The KVM switch is programmed to emulate keyboard, video and mouse initiation commands in accordance with one of any number of different KVM standards, such as Sun, PS2, etc. for keyboard/mouse, and VGA, SVGA, etc. for video. In addition, the KVM switch 12 polls the workstation requirements (such as the type of mouse, type of monitor, and type of keyboard) and provides data conversions that are necessary for otherwise inconsistent keyboard, video, and mouse devices to communicate with the servers 13.
With the introduction of large numbers of computers, the need for a network operator to access many thousands of computers becomes acute. Of course, KVM switches can be scaled in increasing numbers in order to accommodate the growing numbers of computers that must be attached to a few workstations, but the number of scaled KVM switches becomes a space consideration even in large server areas.
Still referring to FIG. 1, an exemplary KVM switch system is shown in FIG. 1 and generally indicated at 10. A plurality of servers 13 are connected to a KVM switch indicated at 12. A user at 11 is capable of controlling each of the servers 13 through KVM switch 12. The operation of the server and the communication protocol used by the switching system 10 are well-known and therefore will not be repeated here for the sake of clarity. It will be appreciated that many different protocols can be employed for the servers 13 to communicate with the switching system 10 and that many protocols will be developed in the future to increase efficiency of data travel on the network and encompassing by the servers 13. The present invention is not limited to any particular one.
FIGS. 2-5 show various prior approaches for eliminating bulky cabling. Specifically, FIG. 2 shows a rack level server access in the KVM switch environment. FIG. 3 illustrates an approach as indicated at 30 that eliminates bulky and cumbersome cabling in rack-type environments. Here, a KVM switch daisy chain approach is shown. This approach includes a plurality of racks such as for example, identified by numeral 33 into which an internal PCI switching card is inserted. Each PCI switching card is located in a respective rack 33. Each PCI card is further interlinked in a daisy chain fashion by a CATS cable to a remote user 31. Each rack 33 includes a server. The configuration shown in FIG. 3 is determined to be feasible to a distance of up to 110 meters. Also, since system 30 occupies a single PCI slot for each server disposed in rack 33, a failure with respect to one server in the rack disables access to some or all servers on the system. Furthermore, system 30 permits a single operator at a time to reach all the servers, and is further restrictive of expansion to an enterprise wide solution.
Referring now to FIG. 5(which is a blowup of a portion of FIG. 4), there is shown another approach for eliminating cable clutter. The system shown at FIGS. 4 & 5, however, works with specific machines. The propriety cable shown in the figure only comes in certain lengths, and therefore the cable must be constructed to service any computer in the rack. As with the prior approaches, any signal failure disables access to some or all network servers. Furthermore, this approach facilitates only one operator at a time to reach the network servers.
Passive extension schemes used in prior systems fail to work in the context of keyboard (K) and mouse (M) information beyond a distance of approximately 20 ft. Beyond this distance, wire extensions for K and M signals become problematic due to inadequate signal rise times caused by cable capacitance. Furthermore, passive cabling systems become bulky when individual wire connections are provided for every required connection.
Although it may be possible to install dedicated communication links to each server computer in order to allow a system administrator to operate the network from a central location, a large number of cables may be required for anything other than a very simple network. Thus, there is a need to overcome the problems encountered by prior systems.
Accordingly, a passive video multiplexing method and apparatus for encoding video synchronization signals within a KVM extension system is proposed to overcome the problems encountered by prior systems.
In the present invention, a Rack Interface Pod (RIP) is provided for receiving video signals from a server computer and providing them to a remote user via a local area network (LAN), preferably an Ethernet LAN. The analog signals received by the RIP are transmitted via Avocent Rack Interconnect (ARI) ports to the Rack Connection Manager (RCM) which includes video processing logic, a supervisory processor, a KVM switch system, and Ethernet interface circuitry. A plurality of ARI systems are connected to the RCM, and a plurality of network servers, intended to be controlled by the remote user, are connected to each ARI by a respective wiring strip or Pod Expansion Module (PEM). The remote user connected to the Ethernet LAN has the capability of selecting a particular network server among the plurality of network servers through the PEM. The remote user is also capable of selecting a particular network server that is directly connected to an ARI port of the RCM. The circuitry located within the RCM (hereinafter “RCM processor” or “digitizing subsystem”) digitizes the KVM signals from a selected network server and forwards the digitized signals to the remote user via the Ethernet LAN. Likewise, the remote users' K and M strokes are passed via the Ethernet LAN to the RCM processor which in-turn passes the signals to the selected network server via the ARI and PEM in the event the network server is connected to the PEM. Remote user's K & M strokes are passed via ARI ports to a network server that is directly connected to the ARI ports.
Each Rack Interface Pod (RIP) includes a processor which emulates K and M signals for a respective network server. Each RIP further provides a mechanism for switching which network server's video signals are passed through the PEM to the RCM. This method of switching video signals is performed by encoding differential R, G, B video signals from a respective network server around a common mode (CM) voltage. Specifically, the common mode voltages are raised or lowered in order to select the active video signal paths from a network server. Each (PEM) further includes a pair of switching diodes per differential video channel for each connection to a common switched differential video channel forming in essence a two pole multiple throw diode switching system. By providing both common mode and differential mode terminations at the receiving end of the bus, individual video channels may be turned on/off by varying the common mode voltages associated with the individual network servers, thus either forward biasing or reverse biasing the switching diodes associated with those channels. If a network server is not selected, then the video source of that particular server, to the PEM, is turned off in the RIP in order to eliminate any capacitive coupling through the reverse biased diodes in the (PEM) and to the RCM.
In the present invention, the Analog Long Interconnect ports provide access by a remote user via either a network based workstation or by direct peripheral attachment through the Analog Internet Protocol Video (IPV) module.
In the preferred embodiment of the present invention, any number of users can communicate on the Ethernet LAN, and any number of servers can be accessed by any of the users. The preferred embodiment provides unlimited scalability while allowing each user to gain console access to any of the associated servers.
In one aspect, the present invention proposes a keyboard, video, mouse (KVM) server management system, comprising a plurality of network interfaces having network ports communicating KVM signals to a plurality of remote user workstations. The remote user workstations are conversely coupled to the network and communicate keyboard and mouse (K, M) signals to a plurality of serves via their corresponding network ports. The KVM server management system further includes a switch for communicating KVM signals between the remote user workstations and a select network server from among the plurality of network servers.
In another aspect, the present invention provides method of switching video signals in a keyboard, video, mouse (KVM) server management system, the method including differentially encoding a plurality of video signal channel from a plurality of network severs around a plurality of common mode voltages; incorporating a pair of diodes in each video signal channels, each pair of diodes connecting to a common differential channel and controlled to switch among the plurality of video signal channels; and selecting a video signal from a select network server from among the plurality of network servers.
In another aspect, the present invention provides a method of encoding video synchronization signals Hsync, Vsync within a keyboard, video, mouse (KVM) extension system, the method including encoding R, G, B video signals differentially around their respective common mode voltage signals, the common mode signals representing encoded functions of combinations of the video synchronization signals; and differentially driving R, G, B video signals so as to allow removal of their respective common mode signals, such that (i) the net of alternating current produced by each of the differential video signals is zero; (ii) the net alternating current produced by encoded synchronization signals is zero.
In yet another aspect, the present invention provides a method of encoding video synchronization signals within a keyboard, video, mouse (KVM) server management system, the method including the steps of providing a plurality of interface ports for receiving KVM signals from a plurality of servers, each interface port including a differential video channel; providing a pair of switching diodes for each differential video channel; multiplexing different video channels down to common differential channels; encoding R, G, B video signals around their respective common mode signals for each differential channel; differentially driving R, G, B video signals and their respective common mode signals, the common mode signals representing functions of video synchronization signals Hsync and Vsync, respectively; switching individual differential video channels by varying common mode voltages of respective individual differential channels, and forward biasing or reverse biasing the switching diodes for enabling or disabling a respective differential channel; and providing both common mode and differential mode terminations at a receiving end of the R, G, B video signals so as to remove common mode signals from the video signals and extract original video synchronization signals.
In another embodiment, the present invention relates to a KVM server management system having a network interface unit, at least one switch to convert native KVM signals from a server into an intermediate format for transmission over corresponding lines, at least one switch communicatively coupled to a least one interface port for communicating K and M signals between a select server among a plurality of servers coupled to the switch via corresponding lines. Each line comprising a plurality of wires, and each wire including a single diode, wherein R, G, B signals are encoded around their respective common mode voltage signals using a sync-on-green encoding on one of the color components in order to select a server among a plurality of servers.
Lastly, the present invention provides a method of interfacing to KVM signals as provided by an Analog Long Interconnect (ALI), an extended distance version of the KVM channel interface with differentially driven R, G, B video with video synchronization encoded on the respective common mode signals and providing corrective frequency compensation for the transmission losses encountered by the R, G, B channels in the extended cabling, as described in prior art, and provides for multiplexing between a plurality of these extensions an interfacing and through a network interface to a remote user.